1. Field
Example embodiments relate to a method of forming a phase change layer using a Ge precursor which may be deposited at low temperature. Other example embodiments relate to a method of manufacturing a phase change memory device using the same.
2. Description of the Related Art
The resistance of a phase change material varies according to the state of the phase change material. The phase change material may have two states: a crystalline state and an amorphous state. In each state, the phase change material has a different resistance. The two states of the phase change material may reverse according to temperature.
A phase change memory device includes a phase change layer formed of a phase change material for storing bit data.
An example of a conventional phase change material is Ge2Sb2Te5 (GST). A GST layer may be formed using a physical vapor deposition (PVD) method. If the GST layer is formed using the PVD method, it may be difficult to control the growth of the GST layer, the deposition speed may be low and densification of the GST layer may decrease.
In order to obtain a higher quality GST layer, a metal organic chemical vapor deposition (MOCVD) method or a cyclic chemical vapor deposition cyclic-CVD) method may be used.
Hereinafter, a conventional method of forming a GST layer in a phase change memory device using a conventional CVD method will be described.
A substrate including a lower layer on which a GST layer is to be formed is loaded into a CVD chamber. The substrate may be heated to a desired disposition temperature. Precursors including metal elements forming the GST layer (e.g., organic metal compound(s) including germanium (Ge), organic metal compound(s) including antimony (Sb) and organic metal compound(s) including tellurium (Te)) may be supplied simultaneously through a shower head to the heated substrate. As the substrate is heated to an appropriate deposition temperature, the supplied precursors are absorbed on the lower layer and decomposed. Metal elements included in the precursors react with the lower layer and the remaining materials in the precursors may be discharged outside of the CVD chamber.
The organic metal compound including Ge may be a quadrivalent compound. The organic metal compound including Ge may have a structure in which four organic ligands are connected to one Ge. The Ge may be located in the center of a tetrahedral. In order to thermally decompose the organic metal compound, a higher temperature may be necessary to heat the organic metal compound because the organic metal compound including Ge is very stable.
The substrate temperature needed to form a GST layer using a conventional CVD method is necessarily high in order that the organic metal compound including Ge may be decomposed. The substrate temperature may need to be substantially greater than 300° C.
In order to increase the integration degree of the phase change memory device, a reset current may be decreased. The reset current may be decreased by filling the GST layer in a narrow contact hole having a diameter of 100 nm or less.
A desired step coverage of the GST layer needs to be secured in the conventional method of forming the GST layer. If using a conventional CVD method, the GST layer needs to be deposited at a substantially low temperature to provide the desired step coverage.
If forming the GST layer using a conventional CVD method, the deposition temperature of the GST layer increases because the organic metal compound including Ge is a quadrivalent, stable compound. It may be difficult to form a GST layer having a desired step coverage to fill a contact hole having a diameter of 100 nm or less.